(1) Field of the Invention
This invention relates to an abrasive molding and an abrasive disc provided with at least one abrasive molding, which are used in a process for abrading, especially abrading, substrate materials such as silicon wafer, an oxide monocrystal substrate, a compound semiconductor substrate, glass substrates, a silica glass substrate and a ceramic substrate, and optical materials.
(2) Description of the Related Art
With the advance of industries including an optical industry and an electronic industry, a higher precision is required for processing material for a magnetic disc, a semiconductor substrate, an optical material and other substrate materials. Thus, there is an increasing demand for obtaining higher smoothness and flatness by abrading the material surface in a lapping step as well as in a polishing step.
In a lapping step, i.e., abrading step before a finishing step, abrading is carried out while an abrading liquid containing a loose abrasive grain is continuously supplied onto the material surface by using a lapping disc. The abrasive grain is composed of, for example, aluminum oxide, iron oxide, chromium oxide, zirconium oxide, silicon carbide or diamond. As the lapping disc, a disc made of graphitized cast iron is widely used.
The conventional lapping step using a loose abrasive grain has a problem such that the loose abrasive grain tends to stick the material surface and thus forming pits thereon. Further, if a loose abrasive grain with a large particle size is used for enhancing the productivity, the abraded surface has a large roughness.
To solve the above-mentioned problems, a proposal has been made in Japanese Unexamined Patent Publication (hereinafter abbreviated to xe2x80x9cJP-Axe2x80x9d) No. 2000-42903 wherein lapping is carried out while an abrading liquid containing a loose abrading grain is continuously is supplied in two stages wherein two kinds of loose abrasive grains having different small particle sizes are separately used. However, the use of two different loose abrasive grains in a single abrading apparatus is troublesome in control of the apparatus. If two abrading apparatuses are used for the two different loose abrading grains, it is also troublesome to transfer the material to be abraded from one apparatus to the other apparatus.
A graphitized cast iron disc has a high hardness and therefore is widely used for lapping. This disc has a problem such that the lapping is difficult to carry out under stable conditions. To solve this problem, an improvement is proposed in JP-A 2000-52238 wherein the size of graphite particles distributed in the cast iron and the density thereof are controlled. In view of complexity an difficulty for controlling the apparatus and process, it is eagerly desired to provide an abrading molding exhibiting a good abrading performance and capable of being used under stable conditions.
A disc made of a high-purity aluminum sintered body and having a flat and smooth surface is proposed in JP-A S52-90900. According to this patent, it is said that an abrading disc composed of an sintered aluminum body having a purity of at least 99% and having a smooth surface with roughness of not larger than 6S is provided. This abrading disc has improved acid resistance, alkali resistance and corrosion resistance as compared with cast iron abrading disc. Further, it is taught in JP-A H1l-239962 that a lapping disk is preferably made of a high-hardness material, and graphitized cast iron, ceramic materials and natural stone are mentioned. It is further taught that ceramic materials and natural stone are especially preferable because of reduced elongation, reduced thermal expansion coefficient, and good acid resistance against an acidic abrading liquid as compared with graphitized cast iron. However, this patent publication is silent on microstructure of ceramic materials and natural stone, and specific lapping performance of these materials.
In view of the foregoing, an object of the present invention is to provide an abrasive molding which is suitable for abrading, especially lapping, substrate materials such as a semiconductor substrate, an oxide monocrystal substrate, glass substrates, a silica glass substrate and a ceramic substrate, and optical materials, and by which a material surface having a high surface precision can be obtained at a high abrading rate and, when a loose abrading grain is used continuously for a long period, a high rate abrading can be stably conduced.
Another object of the present invention is to provide an abrasive disc comprising one or more abrasive moldings having the above-mentioned benefits, which are fixed to a supporting auxiliary.
Thus, in accordance with the present invention, there is provided an abrasive molding composed of a mass of inorganic particles, said mass having pores intervening among the inorganic particles, which molding has abrasive area to be placed in frictional contact with an article to be abraded, and non-abrasive area on a abrading surface of the abrasive molding; said abrasive area having exposed pores having a diameter of not larger than 1 xcexcm, the total area of said exposed pores having a diameter of not larger than 1 xcexcm occupying below 15% of the total area of abrasive area, and the non-abrasive area occupying 20% to 60% of the sum of the abrasive area and the non-abrasive area.
The abrasive molding is preferably made substantially from a powdery inorganic material having a hardness of at least 800 kg/mm2. The inorganic particles preferably consist essentially of alumina particles and stabilizer-containing zirconia particles, wherein at least 60% of the alumina particles have a diameter of not larger than 5 xcexcm and at least 60% of the stabilizer-containing zirconia particles have a diameter of not larger than 5 xcexcm, and the total area (X) of the alumina particles exposed on the abrading surface of the abrasive molding and the total area (Y) of the stabilizer-containing zirconia particles exposed on the abrading surface thereof satisfy the formula:
0.25xe2x89xa6X/(X+Y)xe2x89xa60.95. 
Preferably, at least 20% of the pores exposed in the non-abrasive area has a diameter of at least 10 xcexcm.
The stabilizer-containing zirconia particles has a monoclinic crystal percentage of not larger than 5% and contains yttria as a stabilizer in an amount of 3% to 8% by weight based on the weight of the stabilizer-containing zirconia particles.
In accordance with the present invention, there is further provided an abrasive disc comprising at least one abrasive molding and a supporting auxiliary, said abrasive molding being fixed to the supporting auxiliary.